Pharmacology lecture 4

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Does an antagonist have efficacy?
NO - AR* does not exist
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What does a competitive antagonist do?
Binds and prevents (competes) agonist action but can be overcome with an increased agonist concentration
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What effect does a competitive antagonist have on a agonist-response curve?
It causes a parallel shift to the right
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What does a irreversible competitive antagonist do?
Binds and forms irreversible covalent bonds with receptor
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What effect does an irreversible competitive antagonist have in an agonist-response curve?
Causes a parallel shift to the right and reduced maximal asymptote
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What does a non-competitive antagonist do?
It blocks downstream responses eg. Ca2+ influx
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What effect does a non-competitive antagonist have on a agonist-response curve?
It decreases the slope and max of the curve
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What is the dose ratio?
(Agonist + antagonists EC50)/ agonist EC50
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What is the Shild plot for a competitive antagonist?
r-1 = [B]/kb r=dose ratio B=antagonist conc kb = antagonist dissociation constant Note. Where line intersects x axis = logkb
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What does a pA2 value describe?
The activity of a receptor antagonist. pA2 = -logkb BUT only if relationship is linear and child plot = 1 i.e.. ONLY a COMPETITIVE antagonist
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What is similar to an irreversible competitive antagonist?
Weak partial agonists
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What is the therapeutic index?
Risk:benefit ratio TI = TD50/ED50 or LD50/ED50
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What is TD50?
Therapeutic dose
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What is LD50?
Lethal dose
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What is ED50?
Effective dose
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What does a competitive antagonist do?

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Binds and prevents (competes) agonist action but can be overcome with an increased agonist concentration

Card 3

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What effect does a competitive antagonist have on a agonist-response curve?

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Card 4

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What does a irreversible competitive antagonist do?

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Card 5

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What effect does an irreversible competitive antagonist have in an agonist-response curve?

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